Cells: Plasma Membranes

Vocabulary flashcards covering membrane structure, transport, junctions, receptors, and signaling. Topics include phospholipid bilayer, transport mechanisms, intercellular junctions, and membrane potential.

Phospholipid bilayer

Double layer forming the plasma membrane; hydrophilic heads face water and hydrophobic tails face inward.

Peripheral proteins

Proteins attached to the membrane surface not crossing the bilayer.

Hydrophilic

Water-loving; polar regions (the heads of phospholipids) face aqueous environments.

Hydrophobic

Water-fearing; nonpolar tails face inward away from water.

Selective permeability

Property of membranes to allow some substances to cross more easily than others.

Passive transport

Movement of substances across a membrane without cellular energy use.

Facilitated diffusion

Passive transport via membrane proteins (channels or carriers) down a gradient.

Osmosis

Diffusion of water across a selectively permeable membrane.

Tonicity

Effect of a surrounding solution on cell volume via osmosis.

Isotonic

Solution with equal nonpenetrating solute concentration as inside the cell; no net water movement.

Hypertonic

Solution with higher solute concentration outside; water exits the cell; cells crenate.

Active transport

Movement against a gradient using cellular energy (ATP).

Primary active transport

Direct use of ATP to pump substances across membranes.

Na+/K+ ATPase

Pumps 3 Na+ out and 2 K+ in; maintains ion gradients and resting potential.

Secondary active transport

Uses ion gradients created by primary transport to drive transport of other substances.

Symport

Cotransport where two substances move in the same direction across the membrane.

Vesicular transport

Transport of large amounts via membrane vesicles (endocytosis and exocytosis).

Endocytosis

Process by which cells ingest material through vesicle formation.

Pinocytosis

Non-specific endocytosis of extracellular fluid (cell drinking).

Phagocytosis

Endocytosis of large particles; cell eating.

Exocytosis

Vesicles fuse with the plasma membrane to release contents outside the cell.

Gap junctions

Intercellular channels allowing ions and small molecules to pass between cells for communication.

Tight junctions

Junctions that seal adjacent cells to prevent paracellular transport.

Ligand

Molecule that binds to a receptor to trigger a cellular response.

Receptor

Protein that binds ligands and initiates signal transduction.

G protein

GTP-binding protein activated by a receptor to propagate signals.

Second messenger

Intracellular signaling molecule (e.g., cAMP, Ca2+) that relays signals.

Membrane potential

Voltage difference across the plasma membrane, reflecting ion distribution.

Resting membrane potential

Baseline membrane potential maintained by ion gradients and pumps (often ~ -70 mV).

Ion gradient

Difference in ion concentrations across the membrane essential for transport and potential.

Fluid mosaic model

Membrane structure described as a fluid bilayer with embedded, movable proteins.

Integral (transmembrane) proteins

Proteins that span the membrane and assist in transport, signaling, or channels.

Hydrophobic

Water-fearing; nonpolar tails face inward away from water.

Selective permeability

Property of membranes to allow some substances to cross more easily than others.

Passive transport

Movement of substances across a membrane without cellular energy use.

Diffusion

Movement of molecules down their concentration gradient until evenly distributed.

Concentration gradient

Difference in the amount of substance between two areas.

Hypotonic

Solution with lower solute concentration outside; water enters the cell; cells swell.

Antiport

Cotransport where two substances move in opposite directions across the membrane.

Phagocytosis

Endocytosis of large particles; cell eating.

Exocytosis

Vesicles fuse with the plasma membrane to release contents outside the cell.

Intercellular junctions

Specialized structures that mechanically connect adjacent cells, facilitating adhesion, communication, and sealing of spaces between cells.

Desmosomes

Anchoring junctions that connect cells and resist shear; cadherin connections strengthen sheets.

Cadherins

Calcium-dependent adhesion proteins that link cells at desmosomes.

Second messenger

Intracellular signaling molecule (e.g., cAMP, Ca2+) that relays signals.

Kinase

Enzyme that phosphorylates substrates, amplifying signaling cascades.

Membrane potential

Voltage difference across the plasma membrane, reflecting ion distribution.